1. Field of the Invention
The present invention relates to an apparatus, method and computer program product for aperiodic channel quality indication for carrier aggregation.
2. Related Background Art
The following meanings for the abbreviations used in this specification apply:    3GPP 3rd generation partnership project    CA Carrier Aggregation    CC Component carrier    CIF Carrier Indicator Field    CQI Channel quality indicator    CRC Cyclic Redundancy Check    CSI Channel State information (includes e.g. CQI, PMI and RI)    DCI Downlink Control Information    DL Downlink    DRX/DTX Discontinuous transmission/detection    eNode-B LTE base station (also referred to as eNB)    FDPS Frequency Domain Packet Scheduling    LTE Long term evolution    LTE-A LTE-Advanced    MAC Medium Access Control    MCS Modulation and Coding Scheme    MIMO Multiple Input Multiple Output    NDI New Data Indicator    PDCCH Physical Downlink Control Channel    PMI Precoding Matrix Indicator    PRB Physical resource block    PUCCH Physical Uplink Control Channel    PUSCH Physical Uplink Shared Channel    RI Rank Indicator    RRC Radio Resource Control    SU-MIMO Single User Multiple Input Multiple Output    UE User equipment    UL Uplink
Some embodiments of the present invention relate, for example, to LTE-Advanced system which will most likely be part of 3GPP LTE Rel-10. More specifically, the focus is on Channel State Information (CSI) feedback signalling with carrier aggregation. It is, however, noted that the embodiments may be applied to other systems and releases as well.
LTE-Advanced will be an evolution of LTE Rel-8 system fulfilling the ITU-R requirements for IMT-Advanced. 3GPP approved a new Study Item on LTE-Advanced in RAN#39 (March 2008). Carrier aggregation will be one key technology component required to meet the bandwidth and peak data rate requirements set for the new system.
As described above, embodiments of the present invention relate to component carrier aggregation (or channel bonding), where the total system bandwidth consists of set of component carriers as illustrated in FIG. 3. FIG. 3 shows an example of carrier aggregation with non-contiguous bands, in which the total system bandwidth contains a set of component carriers BW1, BW2, . . . , BWN, having carrier frequencies f1, f2, . . . , fN.
The ongoing standardization of LTE-Advanced in 3 GPP (currently in the study item phase) assumes carrier aggregation to form bandwidths of up to 100 MHz by having aggregation of up to 5 component carriers of 20 MHz each. Different transport blocks with different modulation and coding schemes (MCS) can be transmitted on the different component carriers, although transmitted to the same user. In order to facilitate such schemes with efficient frequency domain link adaptation scheduling, the UEs must provide frequency selective channel state information (CSI) feedback. CSI may include channel quality indicators (CQI), Precoding Matrix Indicators (PMI), Rank Indicators(RI) and/or channel frequency or impulse response and/or channel covariance matrix. Additionally the CSI report may include an indication of the component carrier or the subband the report refers to.
In order to achieve gains from frequency dependent packet scheduling (FDPS) it is necessary to obtain accurate information about the frequency domain behaviour of the propagation channel. To enable FDPS, several frequency selective CSI reporting modes were added into the LTE Rel-8 specifications. The size of the CSI reports depends on the reporting mode, system bandwidth and rank. The maximum size of the CSI report in LTE Rel-8 is 64 bits (mode 3-1, 20 MHz BW, rank >1) excluding CRC bits.
When using multiple component carriers, this would lead to large reports. Hence, the size of the reports should be reduced.